I think Thor wins in a brutal, mountain shattering slog. I think they're pretty comparable strength wise as well as durability. And while, Superman has the speed advantage but I think it's neutralized by Thor being able to shoot lightning from multiple directions and apparently effortlessly. I think the lightning eventually tags Kal-el, and it slows him down enough for Thor to land several massive electrified haymakers like we saw Thor lay on the Hulk, and a massive fully powered bolt of lightning melts the Man of Steel.

cheers,
---the late great Donald Blake

What makes you think Superman and Thor are close in either strength or durability?

Thor's lightning isn't slowing down Superman when he took Doomsday's lightning blast like minor breeze. Not that Superman needs Superspeed here but if he uses Superspeed, the fight would be over before Thor even blinks.